The invention relates generally to devices for enabling reading of videotape time code. It relates specifically to such a device adapted to enable detecting of the time code word prerecorded on each frame of videotape to identify each such frame, for use in videotape production operations including editing, logging, and syncronizing.
The prior art includes devices for reading time code prerecorded on each frame of videotape. However, such devices further shifted the time code signal into shift registers to detect the sync word in the time code and then decoded the time code signal, a relatively complex, expensive, and inefficient method therefor. Such devices further responded and locked on to the input frequency of the time code signal relatively slowly, over a relatively narrow range of videotape speed variations. Further, such devices were unable to read time code from videotape running at uneven speeds, requiring speed stabilization for reading thereof.
Such devices further included a relatively-large number of systems therein for detecting errors in the time code read, thereby making such devices expensive and complex. They further included expensive wideband amplifiers and restrictive phase shift and frequency input requirements in the input circuit. If the azimuth of the videotape recorder head was even slightly out of alignment with the tape, as frequently occurred, accurate reading of the videotape time code was made difficult if not impossible for such devices, and frequent re-alignment of the head was required. Still further, a display of time code as read by such devices, being held on a screen, was subject to being erased by ambient extraneous noise entering the system.